Many carbonaceous materials may contain sulfur as a contaminant. Solid materials such as coals and waxes are known to contain varying amounts of sulfur. Some coals contain sulfur to such an extent that their use is contraindicated because of the polluting effect that burning such high-sulfur coals may have on the environment. The use of petroleum fluids such as oils and gasolines is also subject to restrictions based on their impact on the environment when they are used as fuels.
Petroleum crude oils, for example, such as topped or reduced crudes, as well as other heavy petroleum fractions and/or distillates, including vacuum tower bottoms, atmospheric tower bottoms, black oils, heavy cycle stocks, visbreaker product effluents, bitumens, and the like, are frequently contaminated by excessive concentrations of sulfur. Sulfur is also present in various processed hydrocarbons such as fuel oils and diesel fuels. The sulfur may be present in various combined forms including heteroaroinatic compounds. Removal of these combined forms of sulfur has proven difficult. The sulfur compounds are objectionable because combustion of fuels containing them as contaminants results in the release of sulfur oxides, which are noxious and corrosive, and presents a serious problem with respect to pollution of the atmosphere.
Various processes have been used in the past to remove objectionable sulfur-containing compounds from coal and petroleum. For example, sodium hydroxide or potassium hydroxide solutions have been used to treat petroleum fractions boiling in the general range below about 700.degree. F. Extraction with a liquid solvent, such as sulfuric acid, sulfur dioxide, or furfural has also been used, as has adsorption on suitable materials, such as activated bauxite, charcoal, or clay. Mercaptans have been converted into disulfides and polysulfides by plumbite treatment or treatment with hypochlorite or copper salts. Many catalytic processes generally utilizing hydrogen under pressure have also been developed.
Each of the prior art methods is more or less satisfactory for removing a portion of the sulfur-containing, contaminants from carbonaceous materials. However, none has been devised which is effective to remove substantially all of the sulfur which is present as a contaminant.
It would be desirable to provide a process which is effective for removing sufficient sulfur from coals and petroleum fractions contaminated with sulfur-containing compounds to result in a product containing, for example, less than about 1% sulfur. Since petroleum fractions, such as heavy crudes, may contain as much as about 8-12% sulfur, such a process would represent removal of about 85-95% of the sulfur contaminant in such petroleum fractions.
It is accordingly an object of the present invention to provide a process which is effective to remove a substantial proportion of the sulfur which contaminates various carbonaceous materials.
It is another object of the present invention to provide such a process which utilizes readily available reactants.
Another object of this invention is to provide a process which can be operated at moderate temperatures and pressures.
A further object of the present invention is to provide a process for desulfurizing coals, petroleum products, and other sulfur-contaminated carbonaceous materials, which process is economical to operate and requires a minimum of specialized equipment.
Other objects and advantages of the present invention will become apparent during the course of the following detailed description and disclosure.